The present invention relates to caps having an antitheft lock for fastening members, such as bolts or nuts, having a polygonal engaging portion, and more particularly to a cap having a noval structure and equipped with a lock for preventing a motor vehicle wheel or battery or a lamp on the roof of a four-wheel drive motor vehicle or like part from being stolen by a third party who stealthily loosens the bolt or nut fastening the part.
The term "front" as used herein refers to the left-hand side of FIG. 1 which is closer to the worker when he removes the cap from the nut or attaches the cap thereto, and the other side is referred to as the "rear."